GCC 8.1 includes Gfortran 8.1, which adds
-std=f2018 option, which is a
on enforcing/allowing Fortran 2018 standard.
Gfortran 8.1 can be obtained from the Ubuntu-test PPA.
However, note that libraries such as HDF5 etc. will have to be recompiled to work Gfortran 8.1
At the moment, Gfortran 8.1 can be used to do a rough check of Fortran 2018 standard correctness for commonly uses syntax.